THE STUDY OF GASES 



tflass retort r (Fig. iqa) luted securely to a gauge ab, 

 standing in a trough of water xx. The gauge was 



made from a long- 

 necked flask, 

 pierced at the 

 bottom to admit a 

 syphon-tube y, by 

 means of which air 

 could be drawn 

 out and water 

 sucked up as far 



"IG. 19 (a) HALES'S APPARATUS FOR MEASURING THE 

 VOLUME OF GAS SET FREE BY HEATING ANIMAL, 

 VEGETABLE, AND MINERAL SUBSTANCES. 



as z. The fall or 

 rise of the level 

 of the water in the 

 j;auge, after heating the contents of the retort, showed how 

 much air had been liberated or absorbed. 



This apparatus had the disadvantage that the joint at a 

 T vas liable to leak, 

 especially when an 

 iron retort had to 

 1) e used for 

 stronger heating, 

 or when the gas 

 had to be kept 

 for several days 

 before its volume 

 became constant. 

 These diffi- 

 culties were over- 

 come in a second 

 form of the ap- 

 paratus (Fig. 19^). 

 This consisted of 

 u retort rr made 



an iron gun- FIG. i 9 -(J) HALES'S APPARATUS (Improved design). 



